That's the sad thing about closed source software. Their implementation might be drastically different. I think they should write a blog post or at least a comment here about it though, I'm going to bug them now.

We use base 24, actually, but since we truncate before concatenating, we behave as expected here, unlike Gecko/WebKit. Obviously, a different TC that depends on one selector having more class names than another ("c" in CSS 2.1 6.4.3) will fail in Opera; it passes in GeckKit. See attachment at http://lists.w3.org/Archives/Public/www-style/2012Aug/0493.h... for an illustration.